[linux-dvb] Re: vbv delay/buffer overflows on VBR statmux

[Oliver Endriss <o.endriss@gmx.de>]

Gregor Lawatscheck wrote:
> More importantly it seems something is going wrong with the way
> bitrate information is read and processed from the sequence header.
> Most of the recodings locking up the av7110 here have a bitrate of
> 6480000 bps. Something to bear in mind: The bitrate expressed in the
> normal sequence header is in units of 400 bits/second! So for 6480000
> bps a figure of 16200 would be encoded in the 18 bits of the sequence
> header:
> http://www.mpucoder.com/DVD/mpeghdrs.html#seq
>
>  From what I can make out the bitrate field in the normal sequence
> header suffices to describe bitrates of up to a 100 Mbit - only if
> it's greater the field in the extension header (01B5) is used?

Yes, the bit_rate field in the sequence extension is 0 for all 
recordings I've checked so far. 

> >I have an old RTL recording which cannot be replayed with the
> > current firmware. But it plays fine with the 0.9.4 firmware +
> > current driver. After patching the data stream as indicated above
> > the recording plays flawless with the current firmware.

In my recording, bytes 8-10 of the sequence header are encoded as
0f d2 23, which is bitrate '0000 1111 1101 0010 00'b = 16200!
Same bitrate as Gregor encountered.

> Yes, we're guessing something might go wrong with the bitshifting or
> calculation used to determine an internal buffersize for the bitrate
> which then under certain conditions overflows. We'd appreciate if
> this could be checked in the firmware to resolve this deadlock.

I checked some other recordings which don't show that problem. There is 
a much higher value in the bitrate field: 15 Mbit seems to be a common 
value.

Then I modified pes_play() to patch the bitrate in the sequence header 
and the RTL recording plays flawless...

Oliver


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